It is widely accepted in popular culture that "too much" blinking of the eyes during questioning is a telltale sign that the subject is being deceptive. Body language experts often point to a person's blinking patterns as an indication of lying. The psychology behind this reasoning is that blinking of the eyes is one of many signs of nervousness (others include sweating, fidgeting or refusing to make eye contact). Proponents of this theory reason that a person who is lying is nervous about the deception and cannot control certain physical and/or neurological reactions that result from the stress of deception.
An alternative school of thought is that blinking does, indeed, indicate deception but a person who is lying blinks less frequently, not more frequently. Possible explanations include the hypothesis that a person who is knowingly deceiving a questioner is concentrating more deeply than usual. "People who are lying have to think harder, and when we think harder we tend to be a lot stiller, with fewer movements, because we are concentrating harder," said Dr. Samantha Mann, a Portsmouth University psychologist.
A 2010 study by researchers at Portsmouth University measured the eye blinks of 26 participants in a controlled environment. The study concluded that those who were lying displayed fewer eye blinks when being deceptive compared with when they were answering questions honestly. Those who were truthful exhibited no significant change in blinking patterns.
Talk shows and cable news shows often feature experts who analyze the body language of celebrities or political figures to draw conclusions about deception. But many of these experts are careful to note that sometimes a person's blinking pattern right before or after lying---but not during the lie---is crucial. Some scientific data backs up this view. But the subtlety of this analysis is often lost on the general population because of the popular belief that "blinking equals lying." As more research is conducted, it becomes apparent that analyzing one's blinking is much more complicated than a numbers game.
Although the eyes may, indeed, be the "window to the soul," relying on a person's blinking pattern alone may not be the best way to determine whether or not she is being deceptive. Detailed studies focusing only on blinking patterns are relatively rare, though researchers seem to agree that deception has some effect on a person's blinking pattern. Such data should be weighed as only one criterion when measuring a person's physical responses to stressful actions such as lying. The eyes alone don't tell the whole story.